The present invention relates to a programmable controller for detecting an abnormal state of an output signal.
A conventional programmable controller performs sequence control such that a sequence program is stored in a memory therein and a relay or the like of an external device is operated in accordance with the sequence program. When a load resistance of the external device, is small, an element, such as a transistor of an output circuit of a programmable controller, may be damaged. When sequence control is continued even though the element of the output circuit is damaged, normal sequence control cannot be performed. A conventional programmable controller does not have a means for checking such a failure.